[RE-wrenches] Clipping of microinverter output

[Jason Szumlanski]

This has been addressed several times on the list (check the archives). But
the best source on this still in my opinion is Enphase's Module
Right-Sizing white paper. There are regional variations that make a big
difference.

It's not so much about the inverter efficiency. It's about how much extra
energy is produced at lower irradiance levels compared to lost energy from
clipping. Look at the efficiency curve for the M250. It's flat. Efficiency
really doesn't matter.
http://www.gosolarcalifornia.ca.gov/equipment/inverter_tests/summaries/Enphase%20Energy%20M250-72_2LL-S2X_240Vac.pdf

And with PV prices creeping down to seemingly impossible low prices, it's
really becoming less of a factor. 20% more module price may only result in
5% more system price, reducing any disincentive to oversize.

Jason


On Mon, Oct 3, 2016 at 10:20 PM, Mike Kocsmiersky <mikek at spiritsolar.net>
wrote:

> Recently I’ve been concerned about power clipping of micro inverters and
> the design ratio of PV STC array size to inverter.  If I have a 300W module
> going into a 250W micro inverter, there will be times when the potential
> power output is clipped because the micro inverter can’t handle all the
> power.  I’m thinking cold day with 1000W/m2 irradiance.  It is typical
> nowadays to have an STC array size to inverter ratio of 1.2.  Have you seen
> any analysis on how much energy is clipped, vs how much energy output is
> increased by operating at a better efficiency spot on the micro inverter?
> This assumes that the micro inverter performs better when more fully loaded.
>
> Additionally over time the crystalline silicon module will degrade
> slightly as well, reducing the amount of power clipping.
>
>
>
> I welcome your thoughts.
>
>
>
>
>
> Mike Kocsmiersky
>
> Principal
>
> Phone: 413 883-3144
>
> *Spirit Solar*
>
> www.SpiritSolar.net
>
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>
>
>
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